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Stem airhole diameter

Discussion in 'Pipe Making Forums' started by DGErwin11, Oct 22, 2011.

  1. DGErwin11

    DGErwin11 Moderator Moderator

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    What little bit of sanity I have is struggling to escape. In other words, I am toying with the idea of cutting and drilling my own stems. I notice that on my other pipes, store bought and kits, the air hole in the stems are slightly smaller than the shank air holes. Is there some sort of rule of thumb as to sizing these?
  2. Sasquatch

    Sasquatch Clumsy Poop!

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    Well, yes and no. The rule of thumb is always "make the airway a nice smooth trip for the smoke". This means no big snaggy edges, no big empty chambers, and by and large, the idea that the airway would ever get bigger from bowl to button is shunned. Rather, as the smoke would have to travel relatively faster (and exert relatively less pressure on the walls of the airway) in a thinner airway, the idea is that you make it fattest at the chamber and smallest near the button. Tapered drill bits are handy if you want to take this to the logical extreme.

    I always try to have the airway size on the stem (right at the tenon anyhow) be exactly the same as the size I drilled the stummel with. Usually 11/64, sometimes 5/32.
  3. maddis

    maddis Sales Account

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    Sas, I've read about the goal of making the airway wider at the bowl and taperered toward the button. But if that were taken to its logical end you'd have the mortise going all the way to the bowl, right? So isn't there always going to be a widening from the bowl to the beginning of the mortise, and then (hopefully) a tapering down from there to the button?
  4. Sasquatch

    Sasquatch Clumsy Poop!

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    Let's talk about a perfect pipe, for a second, and ignore some practical realities. In seeking non turbulent airflow, a perfect pipe would have an airway that was one perfectly smooth tube, let's arbitrarily say that it is 5/32" where it connects to the bottom of the chamber. As the tube approaches the button, it gets a little smaller, and also flattens out into what we call the slot - this allows a guy to make a reasonably thin mouthpiece. But in this tube, there are no breaks, no lumps, it's just a smooth tube that changes shape gradually from round and 5/32" across to roughly rectangular and maybe 1/16" high and 1/4" across.

    One school of thought is that the cross-section of this tube should have the same area the whole way down (constant volume) though it changes shape. Another is that the thing should start out big and get smaller and smaller, and then flare out again right at the button. But in both, ideally, you have no or very little in the way of lumps and bumps.

    So when a guy is making a straight pipe, he makes the tenon basically the same length as the mortise, makes sure the holes line up perfect, etc, to make for the smoothest tube he can. In a heavily bent pipe, this is much harder to accomplish, and while there are some cool tricks to get around it, you usually wind up compromising the perfection of the airway in some way or another. In theory, if you do this wrong (or just right), you'll get a lot of condensation because of the turbulence caused at the joint between the stem and the mortise. Peterson System pipes are the extreme version of this, intentionally causing condensation (and catching it) with a tortuous air path.

    The exact measurements, the "right size" for any of these ideas is certainly disputable. Rick Newcombe basically suggests that all pipes be opened up to almost 3/16" at the bowl, most american carvers use 5/32". Ashtons are larger, Ferndowns smaller. And they all smoke.
  5. shadow

    shadow Active Member

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    Hi everyone!
    I have opened ALL the airholes on my pipes to 3/16"... with the exception of two meers, which are a bit delicate, and my cobs, which came with a bigger airhole anyway.
    The results were fantastic! Every single pipe has improved! No more tugging, no more hot smoking, even re-lights are a rarity now!
    Some of my Estates, where the airhole was badly caked up, needed drilling anyway to make them smokable but I generally leave the stems the way they are.
  6. DGErwin11

    DGErwin11 Moderator Moderator

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    Sas,
    If I am reading you right, it seems that the best method would be to use a tapered bit long enough to drill the entire length of the stem in one pass. Since my drill press has only 2" spindle travel, would it be OK to drill 2", lift the spindle, drill bit and rod as a unit, reclamp and finish drilling to desire length?
  7. Sasquatch

    Sasquatch Clumsy Poop!

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    I drill to about an inch of the end with the tapered bit, and then you have a choice of either using a really long 1/16" bit to finish the hole out the other end, or flipping the workpiece and drilling in from the other side.

    You want to keep the bit end as thin as possible in all your drilling operations.

    Now, for your 2" of travel, you may find that you have to re-set the bit or just finish the hole with a hand drill. I use a cordless Makita extensively.
  8. WayneTeipen

    WayneTeipen Member

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    The stems on pipe kits are pretty much always premolded with small airways. It's best to redrill them the same as you would when making your own stems from rod stock in the manner Sas describes above. Since you're drill press only has a 2" travel, I would recommend drilling as far as you can with it then removing the rod from your drill press vise and drilling the rest of the way by hand on the drill press. The part you already started should guide the bit the rest of the way if you eyeball it to keep the drilling relatively straight. Drill at a low speed, keep a decent grip on the rod, and clear the flutes often and you should be fine.
  9. WayneTeipen

    WayneTeipen Member

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    Oh, and I drill my airways to 5/32" most often these days. I drill 9/64" when doing airway acrobatics on some pipe designs. And, on request, will drill to 11/64". One of my favorite pipes is drilled to 11/64". The only thing I don't like about an airway that big is that I get tobacco bits in my mouth on first light but they smoke great.
  10. Sasquatch

    Sasquatch Clumsy Poop!

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    Hold the pipe upside down when you light it, silly.